This invention relates to Visual Message Waiting Indication (VMWIs) circuitry and more particularly to a VMWI device that intelligently detects both CLASS signals and stutter dial tones which are used by telephone companies to alert users regarding the status of their voice mail box.
Regional Bell Operating Companies (RBOCs) and Local Exchange Carriers (LECs) provide central office (CO) based voice mail services to business and residential customers. A shortcoming of these services has emerged over the past few years as the service has reached over 12,000,000 voice mail subscribers. The most frequent subscriber complaint concerning these voice mail services is the lack of visual notification. Currently, voice mail services provide notification to the user with a stutter dial tone. The user must physically pick up the phone and listen for the stutter dial tone. A preferred method would be visual notification that voice messages are in the user's mailbox. A second form of notification is based on a CLASS (Custom Local Area Signaling Services) signal that is transmitted to a subscriber's location and requires a CLASS VMWI detection device.
Stutter dial tone detection on the public phone service was approved by the Federal Communications Commission (FCC) with some limitations on Sep. 28, 1995. One important limitation is a ban on periodic sampling of the phone line. This limitation means that stutter-based VMWI may not detect messages forwarded from another voice mailbox. Other FCC limitations also prevent a stutter detection device from detecting messages cleared by a user from a remote telephone.
The limitations of FCC-approved stutter detection has motivated many telephone companies to offer a second signaling service. VMWI is one of the services defined by the Custom Local Area Signaling Services (CLASS.sub.TM) specification. CLASS VMWI is based on Frequency Shift Keying (FSK) signals transmitted from the CO whenever new messages are present in the user's voice mailbox and when messages are saved or deleted. CLASS VMWI has few of the limitations imposed on stutter dial tone VMWI. However, CLASS VMWI has several unique problems which can affect reliability.
If a user is on the telephone for a long period of time in a CLASS signaling environment and the CO switch attempts to send a CLASS VMWI signal, the CO switch will recognize that the telephone is off-hook and automatically reschedule the CLASS VMWI signal transmission for a later time. The interval before the CLASS VMWI signal is retransmitted may be as long as 30 minutes. If the user is constantly on the phone, the CLASS VMWI signal could be rescheduled almost indefinitely. As a result, detection of a CLASS VMWI signal could be significantly delayed.
Tests have proven that the CLASS VMWI signal is often blocked when a telephone line is connected to the CO through a Subscriber Loop Carrier (SLC). Stutter dial tone signaling is unaffected by SLCs.
VMWI circuits require a large amount of power to continuously detect either stutter dial tone VMWI or CLASS VMWI. Additional power is required to activate the visual indicator that reflects a waiting voice mail message. Standard A.C./D.C. power adapters must be connected to a wall socket that may be inconveniently located away from the telephone socket. A.C. power is also more susceptible to temporary outages and power transients than alternative D.C. battery supplies.
Accordingly, a need remains for an energy efficient VMWI circuit that identifies voice mail status more quickly and reliably in a wider variety of telephone systems.